Heretofore, an active ray curable composition, which is cured by active energy rays such as ultraviolet rays and electron rays, is utilized in practice for various applications such as paints, adhesives and printing ink on such as plastics, paper, woodwork and inorganic materials, a printed circuit board and electric insulation related matters.
Further, as an ink system via ink-jet image formation utilizing these polymerizable compositions, there are known ultraviolet curable ink-jet inks which are cured via ultraviolet rays, and an ink-jet method utilizing this ultraviolet curable ink has attracted attention in recent years with respect to quite rapid drying and recording capability on a non-ink-absorptive recording medium. However, ultraviolet curable ink-jet ink, which contains a pigment (in a dispersion), a photo-initiator and a polymerizable compound, is not stably ejected over a long duration due to problems such as precipitation of the initiator and dispersing agent, as well as a problem of gelation of a polymerizable compound, making it almost impossible to continuously and stably form highly precise images.
Further, ink utilizing a cationic polymerizable compound is easily affected by water content (moisture) at the molecular level, making it difficult to eject the ink stably over a long duration in varying environments (such as temperature and humidity), (please refer, for example, to Patent Documents 1-3).
Further, disclosed has been a technology to utilize a basic compound in ink (for example, please refer to Patent Document 4), however, that technology exhibited problems such as insufficient photo-curing and easy generation of abrasion marks on the printed matter due to softness of the cured layer when an amine compound is simply utilized to maintain ejection stability. Further, a technology to utilize quaternary ammonium salt in the ink has been disclosed (for example, please refer to Patent Document 5), however, the technology exhibited the problem in which it was impossible to maintain stable ejection over a long duration and a large amount of added quaternary ammonium salt is required (as much as approximately 1.0 weight % of the ink) to cause precipitation upon cooling at such as −20° C. in the case of utilizing a quaternary ammonium salt, which is referred to being preferable in the literature and is utilized also in the examples.
[Patent Document 1] Unexamined Japanese Patent Application Publication No. (hereinafter, referred to as JP-A) 2002-188025
[Patent Document 2] JP-A 2005-113043
[Patent Document 3] JP-A 2006-37021
[Patent Document 4] JP-A 2003-341217
[Patent Document 5] JP-A 2004-2668